Exhaust system in an implement driven by internal combustion engine

ABSTRACT

An exhaust system for an implement, especially hedge clippers, trimmers, brush cutters, chain saws and the like, driven by an internal combustion engine, comprising an exhaust pipe for receiving exhaust gas from the engine, wherein the exhaust pipe has an outlet end opening out into the atmosphere, and a circumferentially extending condensate-guiding element disposed on the internal wall of the exhaust pipe, wherein the condensate-guiding element narrows the flow cross-section of the exhaust pipe.

The instant application should be granted the priority date of Nov. 26,2004, the filing date of the corresponding German patent application 102004 057 110.4-113.

BACKGROUND OF THE INVENTION

The invention relates to an exhaust system in a manually operatedimplement driven by an internal combustion engine.

Manually operated implements such as hedge clippers, trimmers,brushcutters, chain saws and similar devices are driven by internalcombustion engines which are equipped in standard designs withtotal-loss lubrication systems. In two-stroke engine designs, inparticular, the fuel/air mixture introduced into the engine contains alow lubricating oil content which, after passing through the engine, isdischarged into the environment as a fine mist together with the exhaustemissions also created. In addition to the aforementioned oil mist,combustion residues, atmospheric moisture and other similar products mayalso lead to mist formation, a phenomenon which can also be observed infour-stroke engines.

It has been shown that the aforementioned substances in the exhaust gasstream tend to form a film of condensate on the internal surfaces of theexhaust system. In certain designs the film of condensate can beobserved being transported in the direction of the exhaust gas stream.Condensate is able to collect in the area of the outlet end of theexhaust pipe and then either drip from the outlet end or even run backalong the outside of the exhaust pipe towards the engine. This leads tounpleasant fouling which requires the implement to be cleanedfrequently.

The object of the invention is to improve an exhaust system of theaforementioned type in such a manner that the fouling effect is avoided.

In the proposed exhaust system for an implement driven by an internalcombustion engine there is positioned on an internal wall of the exhaustpipe a circumferentially running condensate guide element which narrowsthe flow cross-section. The position of the circumferentially extendingcondensate guide element impedes the movement of the film of condensatein the direction of the exhaust gas stream. The condensate guide elementextends radially inwardly from the internal wall of the exhaust pipe.Condensate which has collected or been deposited on the walls of theexhaust pipe builds up in this area and is directed radially inwardly.At the same time, because it extends radially inwardly, thecircumferential condensate guide element reduces the free flowcross-section. As a result, the speed of the exhaust stream is increasedlocally. Due to the increased flow speed, condensate which has collectedand been directed inwardly is carried along by the exhaust gas streamand discharged into the environment. The condensate is thus preventedfrom dripping out of the exhaust pipe.

In an advantageous development the exhaust pipe is connected downstreamof a muffler with the condensate guide element being located in asection of the pipe outside the muffler. Hot exhaust emissions do notflow around this section of the exhaust pipe. The comparatively coolenvironment favors the formation of condensate. The position of thecondensate guide element in this area causes the condensate substance tobe reintroduced into the exhaust gas flow almost directly at the placeof condensate formation.

The formation of large collections of condensate and the associated riskof droplet formation is reliably avoided.

The condensate guide element is advantageously positioned in theimmediate vicinity and upstream of the outlet end. A renewed condensingand depositing of the condensate substance returned to the exhaust gasstream is eliminated.

In a preferred version the condensate guide element forms a separationpoint for the exhaust gas stream in its cross-section. The term“separation point” used here is not limited to an angular edged shape.It covers any aerodynamic shape which narrows the flow cross-section ofthe exhaust pipe and which, in contrast to a venturi-type design,generates flow separation from the surface with subsequent swirlformation. The flow separation caused by the condensate guide elementand the subsequent swirl formation support the effect of the exhaust gasstream as it carries the film of condensate on the walls along with it.

Swirled droplets of condensate are pushed into the inner area of theexhaust gas stream near the center line which makes it harder forfurther deposits to occur on the succeeding pipe walls.

In a useful development the condensate guide element runs in a spiralshape along the internal wall of the exhaust pipe. The spiral shapewhich extends axially permits a restricted degree of axial movement ofthe film of condensate deposited on the walls and thus its distributionover the axial length of the condensate guide element. Distributed overits length, the condensate guide element is able to return the depositedcondensate to the exhaust gas stream with greater efficiency. Somewherein the region of two to six spirals inclusive, and in particular adesign featuring some four spirals, have proved useful in creating asufficient flow direction effect at small volumes.

In an advantageous design the downstream end of the condensate guideelement is located in the area of a center line of the exhaust pipe.Residual condensate which has not been returned the length of thecondensate guide element into the exhaust gas stream, runs in thedirection of flow of the exhaust gas along the condensate guide elementto its downstream end. Here it is located in the area of the center linewhere it can be better removed from the exhaust gas stream anddischarged. The formation of condensate residues is avoided.

In a useful version the condensate guide element is designed as aspiral-shaped wire spring. The circular shape of the wire cross-sectionhas proved effective both in collecting the stream of depositedcondensate and in directing the flow of the exhaust gas stream andforming swirls. These advantageous effects are matched by a simple andcost-effective design.

The upstream end of the wire spring is preferably bent radiallyinwardly. The inwardly bent wire end can easily be used as an assemblyaid. At the same time, the end of the wire which projects into the flowcross-section helps to form swirls and thus to improve the reabsorptionof the condensate.

In an advantageous design the wire spring is held pre-tensioned radiallyin the exhaust pipe. In addition to reliable positioning, this radialpre-tensioning also ensures the application of a radial force pushingthe spring and the internal wall together. A sealing effect can beobserved in this area. The film of condensate is unable to creep betweenthe wire spring and the pipe wall. In fact, it is diverted radiallyinwardly around the wire cross-section of the wire spring where optimumconditions for reintroduction into the exhaust gas stream prevail.

Embodiments of the invention are explained in greater detail below withreference to the schematic drawings, in which:

FIG. 1 shows an overview of a manually operated implement based on theexample of hedge clippers with an exhaust system illustrated in the formof a block diagram;

FIG. 2 shows a perspective, transparent view of the exhaust pipe of thearrangement illustrated in FIG. 1 with details of the condensate guideelement positioned therein;

FIG. 3 shows a section through an enlarged schematic view of the flowconditions in the area of the wire cross-section of the condensate guideelement in the arrangement illustrated in FIG. 2;

FIG. 4 shows a perspective, detailed view of the condensate guideelement as illustrated in FIG. 2 in the form of a wire spring; and

FIG. 5 shows a variant of the wire spring illustrated in FIG. 4 with oneend drawn into the area of the center line.

FIG. 1 shows a perspective view of a manually operated implement basedon the example of hedge clippers which is driven by an internalcombustion engine (1). Instead of hedge clippers, the implement inquestion might also be a brushcutter, a parting-off grinder or a chainsaw, for example.

The internal combustion engine (1), which is not illustrated in greaterdetail, is held in a housing (17) and is almost completely covered bythe housing (17). All that can be seen of the internal combustion engine(1) in the view shown here is a spark plug connector (20) and a crankhandle (19) for starting the internal combustion engine (1).

A front handle (15) and a rear handle (16) are provided for guiding thehedge clippers by means of which a shearing blade (18) driven by theinternal combustion engine (1) can be guided along the foliage to becut.

In the embodiment shown, the internal combustion engine (1) is atwo-stroke internal combustion engine with total-loss lubrication inwhich a portion of lubricating oil is mixed with the fuel for operation.It is also possible to provide separate lubrication with a separatelubricant reservoir and an at least approximately loss-free lubricationsystem, in a four-stroke engine, for example.

The exhaust emissions created when the internal combustion engine is inoperation are discharged into the environment by an exhaust system whichis covered by the housing (17) and indicated in the illustrated by meansof a block diagram. For this purpose, the exhaust system comprises amuffler (7) downstream of which is connected an exhaust pipe (2). Astream of exhaust gas indicated by means of an arrow (3) passes throughfirst the muffler (7) and then the exhaust pipe (2) until it dischargesinto the environment at the free outlet end (4) of the exhaust pipe (2).In order to create the flow-conducting connection, an inner pipe section(9) of the exhaust pipe (2) projects into the muffler (7). A pipesection (8) of the exhaust pipe (2) positioned downstream of this runsoutside the housing of the muffler (7). Positioned in the outer pipesection (8) in the immediately vicinity and upstream of the outlet end(4) is a condensate guide or condensate-guiding element (6) which isdescribed in greater detail below.

The exhaust pipe (2) shown in FIG. 1 is illustrated in an enlarged andtransparent form in FIG. 2. The exhaust pipe (2) has a circularcross-section and runs along a center line (12). Positioned at theoutlet end (4) is the condensate guide element (6) which is designed asa spiral shaped or helical wire spring (14) in the embodiment shown. Thespiral-shaped wire spring (14) or coil spring is inserted radiallypre-tensioned into the free end of the exhaust pipe (2) near the outletend (4). Due to the radial pre-tensioning force, the wire spring isfixed in position in both a frictional and positive fit and conforms tothe internal wall (5) of the exhaust pipe (2) on the inside. The exhaustpipe (2) is also provided with an axial retainer (21) at the outlet end(4) to fix the position of the wire spring (14) axially.

Upstream of the condensate guide element (6), the exhaust pipe (2)provides the exhaust gas stream (3) with an undisturbed, circular flowcross-section. This flow cross-section is narrowed several timescircumferentially and radially inwardly by the wire spring (14) whichrises up from the internal wall (5).

The flow conditions at the condensate guide element are shown in anenlarged, schematic view in FIG. 3. The circular cross-section of a wire(22) of the wire spring (14) (FIG. 2) is pressed against the internalwall (5) of the exhaust pipe (2). The course of the exhaust gas stream(3) is shown by means of flow lines. In the interests of clarity onlytwo (27) of these flow lines, located near the wall, are shown in thedrawing. A film of condensate (23) has formed on the internal wall (5)upstream of the wire (22). Due to the interaction with the exhaust gasstream (3) and in some cases under the effect of gravity, the film ofcondensate (23) endeavors to migrate in the direction of the exhauststream (3) towards the outlet end (4) (FIG. 2). The view shown in FIG. 3illustrates how as a result the film of condensate (23) builds upupstream of the wire (22) and is directed away from the internal wall(5) towards the center line (12) by the condensate guide element (6)(FIG. 2).

The aerodynamic shape selected for the circular cross-section of thewire (22) causes a break in the laminar flow of the exhaust gas stream(3). Downstream of the maximum distance to the internal wall (5), aseparation point (26) is formed after which the flow separates off fromthe surface of the condensate guide element (6) and the subsequentsection of the internal wall (5). Thus the swirls (25) indicated areformed. Once a significant portion at least of the exhaust gas stream(3) close to the wall downstream of the condensate guide element (6) hasformed swirls, the separation point (26) formed in relation to thecross-section of the wire (22) manifests itself as a separation linealong the length of the wire material. Instead of the circularcross-section of the wire (22) shown, other, for example angular,cross-sectional shapes may be useful for the formation of an aerodynamicseparation point (26).

The narrowing of the free flow cross-section due to the condensate guideelement (6) causes a local acceleration of the exhaust gas stream (3)which is shown in the illustration by means of the decreasing distancebetween the flow lines (27) and which reaches its maximum valuesomewhere in the area of the maximum radial lifting or elevation of thecondensate guide element (6) from the internal wall (5). The exhaust gasflow (3) and/or the weight direct the film of condensate (23) around thecross-section of the wire (22) into the aforementioned area. Here thehigh flow speed in conjunction with the separated swirls (25) lead tothe break-up of the film of condensate (23) into individual drops (24)which are carried along by the exhaust gas flow (3) before they have achance to precipitate out on the internal wall (5) again. The separationpoint (26) and the drops (24) are positioned a certain radial distancefrom the internal wall (5) which helps to avoid renewed depositformation.

FIG. 4 shows an individual, perspective view of the wire spring (14)illustrated in FIG. 2. The wire spring (14) usefully comprises some twoto six screw-like spirals (10). The embodiment shown illustrates aspiral (14) with slightly more than four turns. The wire spring (14) isalso curved radially inwardly at its upstream end (13) as a result ofwhich the end (13) projects inwardly into the flow cross-section of theexhaust gas flow (3) (FIG. 2).

A variant of the wire spring (14) shown in FIG. 4 is illustrated in FIG.5. Its downstream end (11), seen in the direction of flow of the exhaustgas stream (3) (FIG. 3), runs from the section of the spiral (10) at thecircumference radially inwardly as far as a longitudinal axis (28) ofthe wire spring (14). There the downstream end (11) is bent in thedirection of the longitudinal axis (28). When installed, the spirals(10) run in a spiral against the internal wall (5) of the exhaust pipe(2), as is also the case in the embodiment illustrated in FIGS. 2 and 4.Here the longitudinal axis (28) coincides with the center line (12) ofthe exhaust pipe (2) (FIG. 2). The downstream end (11) of the wirespring (14) thus lies at least approximately on the center line (12) ofthe exhaust pipe (2) or in the center of the flow cross-section of theexhaust gas stream (3). The embodiment illustrated in FIG. 5 correspondsto that shown in FIG. 4 in so far as all the other features andreference numerals are concerned.

In the embodiments illustrated here the condensate guide element (6) isdesigned as a spiral-shaped wire spring (14). A metal strip, a contouredexhaust pipe (2) wall or comparable other designs may also beadvantageous. Instead of a spiral-shaped course, an annularaperture-like design may also be useful, it also being possible topositioned several circular disks one after another in a cascade.

The specification incorporates by reference the disclosure of Germanpriority document 10 2004 057 110.4-113 filed Nov. 26, 2004.

The present invention is, of course, in no way restricted to thespecific disclosure of the specification and drawings, but alsoencompasses any modifications within the scope of the appended claims.

1. An exhaust system for an implement driven by an internal combustionengine, comprising: an exhaust pipe adapted to receive exhaust gas fromsaid internal combustion engine, wherein said exhaust pipe has an outletend that is adapted to open out into the atmosphere; and acircumferentially extending condensate-guiding element disposed on aninternal wall of said exhaust pipe, wherein said condensate-guidingelement is adapted to narrow a flow cross-section of said exhaust pipe.2. An exhaust system according to claim 1, wherein said exhaust pipe isdisposed downstream of, and in communication with, a muffler, andwherein said condensate-guiding element is disposed in a pipe section ofsaid exhaust pipe that is disposed externally of said muffler.
 3. Anexhaust system according to claim 1, wherein said condensate-guidingelement is disposed in the immediate vicinity of, and upstream of, saidoutlet end.
 4. An exhaust system according to claim 1, wherein across-section of said condensate-guiding element forms a separationpoint for said exhaust gas.
 5. An exhaust system according to claim 1,wherein said condensate-guiding element extends helically along saidinternal wall of said exhaust pipe.
 6. An exhaust system according toclaim 5, wherein said condensate-guiding element has about two to sixspirals.
 7. An exhaust system according to claim 6, wherein saidcondensate-guiding element has about four spirals.
 8. An exhaust systemaccording to claim (5), wherein a downstream end of saidcondensate-guiding element is guided in the vicinity of a center line ofsaid exhaust pipe.
 9. An exhaust system according to claim 5, whereinsaid condensate-guiding element is a helical wire spring.
 10. An exhaustsystem according to claim 9, wherein an upstream end of said wire springis bent radially inwardly.
 11. An exhaust system according to claim 9,wherein said wire spring is held in said exhaust pipe in a radiallypre-tensioned manner.